Before, we get into further details about DBMS, let us become aware about various concepts, relating to the database. As we have already developed on idea about database, let us once again look into it. We can look at database as “A collection of stored “Operational Data” which is used by the application, system of an enterprise”.
An enterprise should use a database as it provides a centralized control of its operational data, which is one of the most valuable assets. Let us look at other advantages of using databases:
Data can be easily stored, one can enforce standards of the organisation can be enforced, one can restrict access by providing security mechanisms, data integrity can be maintained, Data Redundancycan be reduced, complex business rules can be enforced, data can be easily validated, so that unwanted data cannot enter into the system.
Not all the data, which is available is important for an organisation, therefore the concept of Operational Data is evolved, which refers to “the data which is generated, processed and needed for operations to be carried on smoothly.
This is different from input/output as input refers to the data entering the system from outside, which may change operational data, but it is not a part of it, where as the output refers to various reports, messages etc., which are derived from the operational data.
To look into operations on data, let us assume that there is only one database (usually, data is stored ino one or more databases). The basic operations data are:
Integration: It is unification of various distinct data files, with any redundancy among those files, partially or wholly eliminated.
Ex. In an Employee Database, we can have a personal details data file and salary details data file. We can eliminate duplicate of the fields in both files, except a joining field, all other fields can be unique.
Sharing: this means that the data may be shared by different users applications, which is a direct consequence of the data integration.
This operation removes the need to maintain redundant files, as one can use existing files to carry on the operations.
The architecture of Database Management System is involved in providing a basic frame work, which is proposed as standard by ANSI (American National Standard Institute). This is a logical structure, so that one can easily understand the working of DBMS. It is dividing into 3 general levels namely:
Internal Level: It is the level which is closet to the physical storage. This level is lowest in hierarchy, but is the basis for all other levels. This level is concerned about the way in which the data is stored.
External level: This level is the level which is closet to the users. This level can be taken as an interface to the users. This level is highest level and is concerned about how the day is viewed by the users. It is that level which determines the way the data is presented to the users.
Conceptual Level: This level acts as an via media between the internal level and external level by linking them. This level is the one which gives the abstract of the entire database, out of which the necessary data can be taken by external level. It acts as a base from where all other users have the view of the data, therefore it is also called as community user view.
It is the internal view, which is very Low-Level Representation of Entire Database.
DBMS uses languages to represent the schema, sub schema and physical layout of data. To understand the functioning of the DBMS let us first understand few basic concepts involved in its working.
Schema: It is the organisation of data in formal manner. To extract data, DBMS uses both logical and physical descriptions. The physical description involves how actually the data is stored and the logical description gives the chart of types of data used, its values etc. This logical description of data is known as Schema.
Sub schema: It is the view of the data item, viewed by the application programmers, i.e., it is that data, which is viewed and used by Application Programs. It is a sub-part of the entire database.
It is that internal memory, which is used by system temporarily to do a given task. It is volatile memory and used only during execution of a program.
DBMS, with the help of operating system retrieves the data requested by the applications programs. While retrieving the data, it considers physical description, Schema and Subsystem of the Dataand the data retrieved is cached in the system buffer from where the application program access, updates, deletes and does any other operations on data. Finally the saved system buffer data is written back to database, with changes if any.
To carry out any of the above functions DBMS uses a data language, which is used to represent schema, sub schema, physical layouts of the data etc. any data language is usually a combination of sub languages like: DDL and DML and DCL.
DDL: it is acronym for Data Definition Language. This is used for defining the data storage structures and formats. Using this part of the data language one can define his own data structures into which one can store data. Any data object which forms a part of database is created using this language. All data objects can be created, altered and deleted using this language.
DML: This is an acronym for Data Manipulation Languages. This data sub language is used for feeding, manipulating the data into already created data objects/structures. Using this language one can feed, manipulate, update, delete etc. This is used for doing various data manipulation operations, giving it, its name.
DCL: It stands for Data Control Language. This is used to implement security schemes onto the data, by controlling the access to the data. This language is used to give the revoke permissions on data, as and when necessary.
Thus, DDL, DML and DCL together forming a data language can help a user to work with a database.
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